There is plenty of wave energy in the sea, and the wave energy is accessible. Because of the accessibility, wave power generation that utilizes wave energy has been studied in various manners so far in our country and foreign countries and some experiments have been conducted actually in the sea. Nevertheless, due to the reasons, such as 1) high costs, 2) extensive safety measures, and 3) blot on the landscape, wave power generation has not spread in earnest.
Some existing inventions that utilize wave energy have been proposed, for example, in Japanese Unexamined Patent Application Publication No. 10-176649 (Patent Document 1) “Wave Activated Turbine Power Generation By Pole Change Induction Generator And Operating Method Thereof”, Japanese Unexamined Patent Application Publication No . 11-201014 (Patent Document 2) “Wave Activated Power Generation Equipment”, Japanese Unexamined Patent Application Publication No. 9-287546 (Patent Document 3) “Turbine For Wave Activated Generation”, and Japanese Unexamined Patent Application Publication No 2001-151192 (Patent Document 4) “Ocean Platform For Monitoring Earth Warming”.
Patent Document 1 describes an existing device, in which the rotational speed of a generator is appropriately controlled to improve efficiency, thus making it possible to increase electric power to be generated. Patent Document 2 describes an existing device, in which a generator is always rotated in one direction by means of a wells turbine, thus realizing simplification of the structure. Patent Document 3 also describes a similar existing device, in which the angles of rotary blades of a turbine or the angles of guide blades are controlled in accordance with the flow of air to always rotate a generator in one direction, thus rendering simplification of the structure and improvement in efficiency of power generation Patent Document 4 describes an existing device, in which a horizontal stabilizer is provided to render improvement in the conversion efficiency of wave energy.
However, the existing devices described in Patent Document 1 and Patent Document 3 require excessively complex mechanism and controlling operation and, therefore, have a drawback in that the costs of construction and maintenance may not be reduced so much. The existing device described in Patent Document 2 also has a drawback in that, because the device is settled on the sea floor, the costs of safety measures for construction and maintenance may not be reduced so much, and, in addition, because disassembly for maintenance is troublesome, it requires a lot of man hours and an extended construction period. Furthermore, it also has a drawback in that trying to increase the efficiency using a wells turbine increases costs accordingly.
The existing device described in Patent Document 4 has a drawback in that, because a platform portion located on the surface of the sea is spherical in shapes it is largely effected by vertical motion of waves, thus impeding collection of wave energy.